fix(parsing): allow a repeated document-end marker

A `...` after a document is already closed (only comments or blank lines since
the last `...`) ends nothing: a repeated document-end marker is valid YAML, so
consume it as a no-op rather than rejecting the stream as an unsupported
multi-document case. A second documentEnd is not emitted, so no phantom null
document is composed, and real content after the marker stays an error.

Fixes suite case M7A3 (parse-level conformance 313 -> 315); adds focused tests.

Sources/Parsing/Scanner.Directives.swift

@@ -20,8 +20,22 @@ extension PureYAML.Parsing.Scanner {
             return true
         }
         if startsWith("...", state.reader), isIndicatorBoundary(state.reader.peek(offset: 3)) {
-            guard !state.isDocumentClosed else {
-                throw PureYAML.Parsing.ParseError.unsupportedMultiDocumentStream(line: state.reader.mark.line)
+            // A `...` after a document is already closed (only comments or blank lines since the
+            // last `...`) ends nothing: it is a repeated document-end marker, which YAML allows. Skip
+            // it as a no-op rather than emitting a second documentEnd (which would compose a phantom
+            // null document) or rejecting a valid stream. Content after it is still an error.
+            if state.isDocumentClosed {
+                state.reader.advance()
+                state.reader.advance()
+                state.reader.advance()
+                while state.reader.peek() == " " {
+                    state.reader.advance()
+                }
+                if let next = state.reader.peek(), !isLineBreak(next), next != "#" {
+                    throw PureYAML.Parsing.ParseError.contentAfterDocumentEnd(line: state.reader.mark.line)
+                }
+                skipLine(&state)
+                return true
             }
             // A `...` ends a document, so a directive still awaiting its `---` never gets one.
             try enforceDirectiveHasDocument(state)

Tests/RepeatedDocumentEndTests.swift

@@ -0,0 +1,30 @@
+@testable import PureYAML
+import Testing
+
+/// A document-end marker (`...`) may appear repeatedly: once a document is closed, a further `...`
+/// (with only comments or blank lines since the last one) ends nothing and is a no-op, rather than
+/// being rejected. Content other than a comment after such a marker is still an error.
+@Suite("Repeated document end")
+struct RepeatedDocumentEndTests {
+    @Test("A second `...` after a closed document, separated by a comment, is a no-op")
+    func test_repeatedMarkerIsNoOp() throws {
+        let documents = try PureYAML.parseStream("a\n...\n# comment\n...\nb\n").map(\.value)
+        #expect(documents == [.string("a"), .string("b")])
+    }
+
+    @Test("A comment-only region between two `...` markers contributes no document")
+    func test_commentOnlyBetweenMarkers() throws {
+        // Mirrors suite case M7A3: a bare document, then `...`, a comment, a repeated `...`, and a
+        // root block scalar as the next document.
+        let yaml = "Bare\ndocument\n...\n# No document\n...\n|\n%!PS-Adobe-2.0 # Not the first line\n"
+        let documents = try PureYAML.parseStream(yaml).map(\.value)
+        #expect(documents == [.string("Bare document"), .string("%!PS-Adobe-2.0 # Not the first line\n")])
+    }
+
+    @Test("Real content after a repeated `...` marker is still rejected")
+    func test_contentAfterRepeatedMarkerRejected() {
+        #expect(throws: PureYAML.Parsing.ParseError.self) {
+            _ = try PureYAML.parseStream("a\n...\n... x\n")
+        }
+    }
+}